The present invention relates to apparatus for forming a web of material into a plurality of individual rolls. More particularly, the present invention relates to a control system for a slitter-rewinder apparatus which insures that light weight stretchable web materials are evenly wound into precise rolls with a minimum amount of material distortion.
Relatively thin sheet materials such as film, foil, paper, laminate and cloth are typically manufactured in the form of wide, long webs, which may measure, for example, six feet in width by one thousand feet in length. Each web is usually wound about an elongate cylindrical supply core for transport and storage. The manufacture of consumer products from such webs, for example rolls of adhesive tape, usually involves the use of an apparatus known as a slitter-rewinder. Examples of this type of apparatus are currently manufactured by Voorwood Company, 2350 Barney Street, Anderson, Calif., 96007 and Arrow Converting Equipment, Inc., Law Drive, Fairfield, N.J., 07006.
Known slitter-rewinder apparatus typically include an upright frame which supports a pair of powered takeup rollers and a supply roller or chuck for rotatably supporting the supply core and supply roll. During the rewinding operation, the web is guided by idler rollers from around the supply core past a series of slitting blades. The resulting strips of web material are rewound about a plurality of corresponding product cores on opposite ones of the takeup rollers in alternating fashion to give the necessary clearance between adjacent product rolls during their formation.
Heretofore, known slitter-rewinder apparatus have typically utilized the powered takeup rollers for pulling the web material from around the supply core. This latter core has not been directly powered but has been rotated only through the pulling action supplied by the takeup rollers. An adjustable drag brake, usually of the disc type, has been utilized to prevent over-spinning of the supply roll. The disc brake has also been used to attempt to maintain the tension necessary for proper slitting and rewinding.
The aforementioned type of slitter-rewinder apparatus is used as follows. The product cores are slid over the takeup rollers with spacers splined to the takeup rollers positioned between adjacent product cores. Pneumatic means are utilized to compress the product cores endwise against the spacers with a predetermined amount of pressure. At the start of the rewinding operation, the supply core is initially fully braked to prevent rotation thereof. The takeup rollers are rotated within the stationary product cores which are held in position because of their attachment to the non-moving strips of the web material. The brake on the supply core is then gradually released manually, or automatically by means of a sensing device known as a dancer roll tension control. Eventually, the friction between the product cores and the spacers is sufficient to cause the product cores to rotate and rewind the strips. The speed of rotation of the product cores increases as the brake is further released.
Heretofore with the type of slitter-rewinder apparatus described above, it has been difficult to precisely control the tension of the web portion extending between the supply and product cores to insure proper slitting and rewinding. This is especially true in the case of lightweight stretchable web materials such as acetate. Generally, a relatively great amount of pulling force and resulting web tension are required to unwind the web from around the supply core. The amount of pulling force required increases as the diameter of the web around the supply core decreases and the resulting leverage is reduced. If the disc brake is released too quickly to compensate for the increased pulling forces required, then over-spinning occurs and the strips of web material weave laterally. The resulting product rolls are not uniformally edge aligned, but instead have a telescoping or other undesirable configuration. If the brake is released too slowly, then the web tension is too great and the material stretches. The resulting product rolls then have a slightly smaller intermediate diameter than edge diameter. When the strips are unrolled from these product rolls, they are distorted and frequently have undulating side edges. This problem is particularly acute where the gauge or the thickness of the web varies across the width thereof. Regions called gauge bands, which extend lengthwise of the web and are of relatively greater thickness, will form high spots on the product rolls when tightly rewound.
In other commercially available slitter-rewinder apparatus similar to that described above a set of rollers between the supply core and the product cores over which the web passes are powered to pull the material from the supply roll. This reduces the tension of the material at the product cores. However, as the product roll diameter increases the slippage between the product cores and the constant rpm takeup rollers increases. This friction generates heat which can damage the web material.
In U.S. Pat. No. 4,238,082 issued Dec. 9, 1980, there is described an improved slitter-rewinder apparatus in which the takeup rollers are rotatably driven by a first electric motor and the supply core check is rotatably driven by a second electric motor. The driving connection between the second electric motor and the supply core chuck includes intermeshing spur and worm gears, which driving connection prevents pulling forces exerted by the web portion extending between the supply and product cores from increasing the speed of rotation of the supply core. An electric control circuit is provided for independently varying the amount of electric current supplied to the first and second electric motors. The speed controls may take the form of rheostats which may be manually adjusted by control knobs. Also disclosed in that patent is a speed control system which includes means for sensing the amount of web that has been wound around the product cores and means responsive to the sensing means for automatically increasing the amount of current supplied to the second electric motor in a predetermined proportion to speed up the supply roll. In one form of the speed control system, a mechanism known as a dancer roll engages the outer surface of one of the product rolls. As the diameter of the product roll increases, the dancer roll arm assembly pivots and a mechanical linkage then transmits the pivoting motion to operate a rheostat or potentiometer to increase the amount of current supplied to the second electric motor and thereby increase the supply roll speed. Product rolls with uniformly aligned edges and without high spots are produced.
The control system described above which is disclosed in U.S. Pat. No. 4,238,082 represents a significant improvement over previous control systems for slitter-rewinder apparatus. However, it would be desirable to provide a system for controlling the supply and product roll speeds in a slitter-rewinder apparatus with even greater precision to further insure that product rolls which are produced with the apparatus have uniformly aligned edges and do not have high spots or material distortion.